Arvind Mamgain

QuBE/Qubex: an integrated hardware-software system for superconducting qubit experiments with broadband control

  1. Akinori Machino,
  2. Kazuhisa Ogawa,
  3. Takefumi Miyoshi,
  4. Hidehisa Shiomi,
  5. Shinichi Morisaka,
  6. Ryo Matsuda,
  7. Nilton F. G. Filho,
  8. Koichiro Ban,
  9. Takafumi Miyanaga,
  10. Keisuke Koike,
  11. Ryutaro Ohira,
  12. Toshi Sumida,
  13. Yoshinori Kurimoto,
  14. Yuuya Sugita,
  15. Yosuke Ito,
  16. Yasunari Suzuki,
  17. Peter A. Spring,
  18. Shiyu Wang,
  19. Hiroto Mukai,
  20. Arvind Mamgain,
  21. Shuhei Tamate,
  22. Yutaka Tabuchi,
  23. Yasunobu Nakamura,
  24. and Makoto Negoro
Achieving high-fidelity operation in large-scale superconducting qubit systems requires not only control hardware with broad frequency coverage, low crosstalk, and tight synchronization
but also software that coordinates system configuration, experiment execution, and data analysis. Here we present an integrated qubit-control system that combines broadband microwave hardware with a pulse-level software stack for scalable superconducting qubit experiments. The hardware provides broadband microwave coverage, including an instantaneous span of up to 1.6 GHz from a control output, while the software reduces setup and calibration overhead through automated configuration and built-in experiment workflows. We validate the system on a 64-qubit fixed-frequency transmon chip through full-chip frequency identification and representative demonstrations, including multi-unit far-detuned cross-resonance calibration and benchmarking that yields a measured two-qubit gate fidelity of 98.34%, and multilevel readout beyond the computational subspace. By disclosing the hardware architecture and releasing the software stack as open source, this work provides an inspectable hardware-software foundation for scalable superconducting qubit control experiments.
arxiv pdf

Characterising Polariton States in Non-Dispersive Regime of Circuit Quantum Electrodynamics

  1. Arvind Mamgain,
  2. Samarth Hawaldar,
  3. Athreya Shankar,
  4. and Baladitya Suri
A superconducting qubit coupled to a read-out resonator is currently the building block of multiple quantum computing as well as quantum optics experiments. A typical qubit-resonator
system is coupled in the dispersive regime, where the detuning between qubit and resonator is much greater than the coupling between them. In this work, we fabricated and measured a superconducting transmon-resonator system in the non-dispersive regime. The dressed states formed by the mixing of the bare qubit and resonator states can be further mixed by applying a drive on the qubit, leading to the formation of polariton states. We report experimental studies of transitions between polariton states at varying driving powers and frequencies and show how the non-dispersive coupling of the higher levels of the qubit-resonator system modifies the polariton eigenstates and the corresponding transition frequencies. We also report close agreement with numerical results obtained from a driven Jaynes-Cummings Model beyond the dispersive regime.
arxiv pdf